Beta particles - smaller and faster: less ionising and penetrate further - stopped by few meters of air or thin aluminium - negative charge and deflected by electric/magnetic fields, opposite direction to alpha particle

Gamma rays - electromagnetic waves: travel long way through material before colliding - weakly ionising, very penetrating - several cm of lead or meters of concrete needed to absorb most of the radiation - not deflected by electric/magnetic fields

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P2.6.5 - Half-Life

Measure radioactivity of sample of radioactive material by measuring count rate from it

Radioactivity of sample decreases over time - how quickly count rate falls to 0 depends on isotope - some take minutes, others millions of years

Half-life used to measure how quickly radioactivity decreases

Half-life: time taken for count rate of original isotope to half

Or defined by time taken for number of unstable nuclei in sample to half

Half-life is the same for any particular isotope

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P2.6.6 - Radioactivity at Work

Alpha sources - used in smoke alarms - not dangerous: poorly penetrating - needs half-life of several years

Beta sources - used for thickness monitering in manufature of paper or metal foil - alpha particles would be stopped and gamma rays would pass through it - needs half-life of several years: decrease in count rate is due to changes in thickness

Gamma and beta sources - used as tracers in medicine - injected or swallowed by patient and progress around body monitered by dectector outside - needs half-life of few hours: patient isn't exposed to too much radiation

Radioactive dating - find out age of ancient material - carbon dating used for wood and other organic material - uranium dating used for igneous rock